The present invention relates to an infrared reflecting blue pigment and an infrared reflecting green pigment which comprise no harmful elements, and are capable of providing a heat-shielding paint exhibiting an excellent infrared reflecting property.
In roads, buildings, storage tanks, automobiles, ships, etc., which are used or located out of doors, an inside temperature thereof is increased when exposed to solar radiation. For this reason, an outside surface of buildings, automobiles, etc., has been painted with a white to light color to reflect sunlight thereon, thereby enhancing a heat-shielding effect to some extent.
However, in particular, roofs of buildings exposed to outside are frequently painted with a deep to black color to make stains or contamination thereon unremarkable. Buildings, automobiles, etc., whose outside surface is painted with a deep to black color, tend to absorb sunlight as compared to those having an outside surface painted with a light to white color, and tend to suffer from considerable increase in inside temperature when exposed to solar radiation. Such a high inside temperature of buildings, automobiles, etc., is undesirable for transportation or storage of products.
From the standpoint of saving energies for preventing global warming problems, it has been strongly demanded to suppress the increase in inside temperature of buildings, automobiles, etc., whose outside surface has deep color to black color. For example, there have been conventionally developed heat-shielding black paints comprising a black calcined pigment having a spinel structure which comprises CoO, Cr2O3 and Fe2O3 (refer to Japanese Patent Application Laid-Open (KOKAI) No. 2000-72990). However, the black calcined pigment comprises harmful Cr. In consequence, it has been demanded to provide an infrared reflecting black pigment comprising no harmful elements which are capable of exhibiting an excellent infrared reflecting property. The present inventors have developed such an infrared reflecting black pigment comprising no harmful elements which are capable of exhibiting an excellent infrared reflecting property, and already filed a patent application relating thereto (refer to Japanese Patent Application Laid-Open (KOKAI) No. 2007-197570).
As is well known, in addition to these black paints, many other coloring paints such as blue, green and red paints have been employed. As the conventional blue inorganic pigments for paints, etc., there have been extensively used cobalt blue-based pigments. With respect to such cobalt blue-based pigments, many proposals have been made to provide various improved blue pigments. For example, there has been proposed the method of producing a cobalt blue-based pigment in the form of reddish fine particles in which hydroxides or carbonates of aluminum and cobalt are precipitated using sodium carbonate as an alkali agent in the co-existence of a phosphorus compound (refer to Japanese Patent Application Laid-Open (KOKAI) No. 2000-80301). Further, there has been proposed the method of producing a cobalt blue-based pigment having a high transparency in which a sufficient energy capable of exhibiting a mechanochemical effect is applied to starting materials upon pulverization and mixing thereof to obtain secondary particles in which cobalt and aluminum are present in a uniformly dispersed state, and then the secondary particles are heated and calcined (refer to Japanese Patent Application Laid-Open (KOKAI) No. 10-219132 (1998)).
In addition, as the green inorganic pigments for paints, etc., there are well known those pigments in the form of a spinel-type composite oxide comprising cobalt, aluminum, chromium and titanium. However, it is also desired that the green pigments comprise no harmful chromium therein. As the chromium-free green pigments, there have been proposed green pigments in the form of a composite oxide comprising oxides of cobalt, aluminum and titanium (refer to Japanese Patent Application Laid-Open (KOKAI) No. 2000-86246).